1. Field of the Invention
The present invention relates, in general, to microwave ovens and, more particularly, to a method and apparatus for controlling an operation of a microwave oven during a cooking process.
2. Description of the Related Art
Microwave ovens are machines which cook food with the assistance of a variety of atmospheric sensors, such as a humidity sensor, a temperature sensor and a gas sensor, in addition to a weight sensor used for measuring the weight of food to be cooked.
The microwave oven starts a cooking process when a user operates a start button, after laying food on a turntable-type cooking tray installed in a cooking cavity of the oven and selecting a desired cooking mode in an automatic cooking menu provided on a control panel. When starting the cooking process of the microwave oven, a microprocessor receives a signal outputted from the humidity sensor, and compares the signal outputted from the humidity sensor with preset reference data stored in a data storage unit, thus calculating a target cooking period so as to control a magnetron in accordance with the calculated target cooking period.
In a conventional method of controlling the microwave oven during the cooking process, a first cooking period is determined such that the first cooking period is terminated at a time when a calculated slope of a sensor output value becomes equal to a preset reference slope. A second cooking period is determined in accordance with the first cooking period and factors preset in accordance with the kind of food to be cooked. At an end of the second cooking period, the cooking process is terminated.
FIG. 1 is a graph expressing a conventional method of controlling a cooking process for microwave ovens. As shown in FIG. 1, the total time for the cooking process of a microwave oven in the conventional method consists of an initial standby period TC, a first cooking period T1, and a second cooking period T2. Thus, when the microwave oven starts the cooking process in a selected cooking mode, a fan installed in the machine room of the oven is operated for the initial standby period TC, of about 20 minutes, at an initial stage of the cooking process, thus reducing the temperature in the cooking cavity to about a predetermined temperature. The first cooking period T1 starts at a time when the initial standby period TC ends, and is terminated at another time when a calculated slope of a sensor output value becomes equal to a preset reference slope “A”. The second cooking period T2 is determined in accordance with the first cooking period T1 and factors preset in accordance with the kind of food to be cooked. In a detailed description with reference to the graph of FIG. 2, the second cooking period T2 is lengthened in proportion to a length of the first cooking period T1. That is, as the first cooking period is lengthened as shown by points T1′, T1″ and T1′″ (where T1′<T1″<T1′″), the second cooking period T2 is proportionally lengthened, as shown by points T2′, T2″ and T2′″ (where T2′<T2″<T2′″). Such a relation between the first and second cooking periods T1 and T2, which is expressed by a function with an ascending slope, is determined in consideration of a weight of food to be cooked. Thus, when food must be cooked having a heavy weight during one period of time, the first and second cooking periods T1 and T2 are controlled to be lengthened since such a lengthening in the first and second cooking periods T1 and T2 is desirable while cooking most kinds of foods using the microwave oven. Data for such an ascending slope-type relation between the first and second cooking periods T1 and T2 is tabulated, and stored in the data storage unit connected to a control unit of a control apparatus. During a cooking process of the microwave oven, the control unit primarily calculates a first cooking period, and secondarily searches the data table stored in the data storage unit, based on the calculated first cooking period, thus determining a second cooking period T2.
However, the conventional method of controlling a cooking process for microwave ovens is problematic in that the second cooking period T2 determined in accordance with the calculated first cooking period may not be suitable for the cooking of some kinds of foods. Thus, when cooking some kinds of foods, such as popcorn, the second cooking period T2 determined according to the calculated first cooking period is not suitable for the cooking of the food.
The cause of the problem is closely related to the kind of food or components of the food to be cooked, in addition to the position of the food in the cooking cavity and deterioration in the microwave irradiating performance of the magnetron. For example, a substantial difference between a calculated cooking period and a practically required cooking period has been experimentally shown even when a second cooking period is determined using the ascending slope-type relation between the first and second cooking periods T1 and T2 while considering the state of food and the content of moisture in the food, in the case of cooking processes of the same kind of food. Furthermore, in the case of some kinds of foods, the second cooking T2 period may be in inverse proportion to the first cooking period T1. Therefore, an improved method of determining the precise period of time for cooking in accordance with the kinds of foods to be cooked is needed.